use PageSizePaginationMixin for CursorPagination

tests for custom page_size in CursorPagination

rest_framework/pagination.py

@@ -487,20 +487,20 @@ class LimitOffsetPagination(BasePagination):
         return template.render(context)
 
 
-class CursorPagination(BasePagination):
+class CursorPagination(PageSizePaginationMixin, BasePagination):
     """
     The cursor pagination implementation is neccessarily complex.
     For an overview of the position/offset style we use, see this post:
     http://cramer.io/2011/03/08/building-cursors-for-the-disqus-api/
     """
     cursor_query_param = 'cursor'
-    page_size = api_settings.PAGE_SIZE
     invalid_cursor_message = _('Invalid cursor')
     ordering = '-created'
     template = 'rest_framework/pagination/previous_and_next.html'
 
     def paginate_queryset(self, queryset, request, view=None):
-        if self.page_size is None:
+        self.page_size = page_size = self.get_page_size(request)
+        if not page_size:
             return None
 
         self.base_url = request.build_absolute_uri()
@@ -540,8 +540,8 @@ class CursorPagination(BasePagination):
         # If we have an offset cursor then offset the entire page by that amount.
         # We also always fetch an extra item in order to determine if there is a
         # page following on from this one.
-        results = list(queryset[offset:offset + self.page_size + 1])
-        self.page = list(results[:self.page_size])
+        results = list(queryset[offset:offset + page_size + 1])
+        self.page = list(results[:page_size])
 
         # Determine the position of the final item following the page.
         if len(results) > len(self.page):

tests/test_pagination.py

@@ -508,6 +508,8 @@ class TestCursorPagination:
 
         class ExamplePagination(pagination.CursorPagination):
             page_size = 5
+            page_size_query_param = 'page_size'
+            max_page_size = 20
             ordering = 'created'
 
         self.pagination = ExamplePagination()
@@ -643,6 +645,24 @@ class TestCursorPagination:
 
         assert isinstance(self.pagination.to_html(), type(''))
 
+    def test_page_size(self):
+        (previous, current, next, previous_url, next_url) = \
+            self.get_pages('/?page_size=10')
+
+        assert previous is None
+        assert current == [1, 1, 1, 1, 1, 1, 2, 3, 4, 4]
+        assert next == [4, 4, 5, 6, 7, 7, 7, 7, 7, 7]
+        assert 'page_size=10' in next_url
+
+        (previous, current, next, previous_url, next_url) = \
+            self.get_pages(next_url.replace('page_size=10', 'page_size=4'))
+
+        assert previous == [2, 3, 4, 4]
+        assert current == [4, 4, 5, 6]
+        assert next == [7, 7, 7, 7]
+        assert 'page_size=4' in previous_url
+        assert 'page_size=4' in next_url
+
 
 def test_get_displayed_page_numbers():
     """